1. Field of the Invention
This invention relates to coated abrasives and to their preparation, and in particular to coated abrasives employing a moisture-cured polyurethane hot melt adhesive as a make coating.
2. Related Art
Coated abrasive products are normally prepared by coating one surface of a substrate with a first binder layer having adhesive properties, often referred to in the art as the "make" coating. Particles of abrasive material are applied to the coated substrate and partially embedded therein. A layer of a second binder, often referred to as the "size" coating, is then applied over the abrasive particles and make coating. The thickness of the second binder layer regulates the amount of the abrasive material extending above the binder medium. Anti-loading materials have generally been included in a further optional layer, referred to in the art as the "supersize" coating.
The adhesives used to form the make coating are generally water- or solvent-based and include phenolic resins, urea-formaldehyde, melamine-formaldehyde and combinations thereof. Other adhesives which have been used are based on animal hide glue and starch. Similar adhesives have been used for the size coating.
Many of the known adhesive systems which have been used in the above constructions are of low solids content requiring a high energy input for drying and the careful selection of backing materials. In the case of solvent-based adhesives, apparatus to extract solvent emissions can also be needed. Such extraction apparatus may also extract the fines from the abrasive particles leading to processing problems.